(1) Field of the Invention
The present invention relates to an abnormality detection of an electrically driven (or an electric) power steering system (or abbreviated as EPS).
(2) Description of Related Art
In an excessive current abnormality monitoring of a motor drive circuit, a current sensor disposed independently of another current sensor used in a motor drive control detects a current caused to flow from a power supply to an inverter circuit. Thus, by setting an abnormality detection threshold value with a current output in a transient response state with respect to a maximum current in a normal use range taken into consideration, the abnormality of the motor drive circuit is monitored.
In addition, in a case where an excessive current abnormality is monitored using a current sensor for the motor drive control in the normal use region in terms of a manufacturing cost reduction demand, the abnormality is detected from an averaged value of the detected current by means of a filter. Hence, a sufficiently high abnormality detection threshold value with respect to the maximum current of the normal use region is set as described in a Japanese Patent Application First Publication (tokkai) 2009-81930 published on Apr. 16, 2009 (which corresponds to a U.S. Pat. No. 7,791,293 issued on Sep. 7, 2010).